Answer: Oral stage
Explanation:
According to the psychoanalyst Sigmund Freud, children tend to go through psychosexual stages that eventually leads to the development of their adult personality.
An erogenous zone is identified as an area that is focused on to serve as a source of pleasure in response to a stimulation.
If at a stage in development certain issues are not resolved, it is said that fixation occurs (Fixation is a focus on an earlier psychosexual stage)and until the individual resolves this conflict, the individual could remain stuck in the stage.
For Greg, he his fixated on the oral stage of the psychosexual stage, with his erogenous zone being the mouth. Oral fixation could lead to problems with eating, drinking, nail-biting or smoking.